A: Power over Ethernet or PoE technology describes a system to safely pass electrical power, along with data, on Ethernet cabling. Standard versions of PoE specify category 5 cable or higher power can come from a power supply within a PoE-enabled networking device such as an Ethernet switch or from a device built for "injecting" power onto the Ethernet cabling.

The IEEE 802.3af PoE standard provides up to 15.4 W of DC power (minimum 44 VDC and 350 mA) to each device. Only 12.95 W is assured to be available at the powered device as some power is dissipated in the cable.

The IEEE 802.3at PoE standard (ratified September 11, 2009), provides up to 25W of power. Some vendors have announced products that claim to comply with the new 802.3at standard and offer up to 51W of power over a single cable by utilizing all 4 pairs in the CAT5 cable. Numerous non-standard schemes had been used prior to PoE standardization to provide power over Ethernet cabling. Some are still in active use.